Alkyl glyceryl ether sulfonate salts, (AGES) particularly the sodium salt, have been well known for their commercial utility in detergent compositions for many years. The synthesis of these materials is relatively straight forward and also known for many years. A review article by David Whyte entitled "Alkyl Glyceryl Ether Sulfonates" appearing in Surfactant Science Series, Vol 7, Anionic Surfactants Part 2, 1976 provides a good summary of synthetic routes. In one synthesis a long chain alcohol is reacted with epichlorohydrin under acid catalysis to form a chlorohydrin ether. Thereafter the chlorohydrin ether is subjected to the Strecker reaction, using sodium sulfite, or bisulfite or a mixture thereof, to form the alkyl glyceryl ether sulfonate salt. Since the Strecker reaction is a two phase reaction, good interphase contact is required as well as an appropriate catalyst according to the Whyte article. The reaction product is a viscous paste and heat transfer is poor. Therefore the water content in the system is a major means of control of peak reaction temperature as well as the system processability, particularly viscosity, by means of the mixing apparatus. Excessive amounts of water lead to undesirably dilute AGES products. Low water content results in high viscosity, low thermal capacity, and poor control on temperature. For AGES with an alkyl chain in the C.sub.12 range an overall water content of 50% or more is suggested for the sodium salt. The greater solubility of potassium sulfite and potassium salts of AGES allows somewhat higher solid levels to be about 60% employed.
Another route to AGES mentioned in the Whyte article is sulfonating a terminal glycidate epoxy ether of the desired structure with a mixture of sulfite and bisulfite salt as shown below. ##STR2##
An even higher solids content can be achieved in this sulfonation reaction of the epoxide according to the review article. However the review article states that difficulties in temperature control and excessive product viscosities make it undesirable to achieve these higher solid levels. In fact high temperatures are used to initiate the sulfonation of the epoxide with the sulfite-bisulfite mixture, 300.degree. F. or less. The lowest temperature used for initiation of the sulfonation of the epoxy in Whyte U.S. Pat. No. 2,989,547 is 275.degree. F., Example 6. In each of the examples in this patent, the continuing reaction is carried out at a significantly higher temperature than the initiation temperature.
Alkoxylated alkyl glyceryl ether sulfonates, hereinafter referred to as NEGS, have been known for many years as well and are disclosed to be useful in secondary recovery processes for increasing production in oil wells. The difference between AGES and NEGS is the presence of one or more alkoxy groups between the last carbon atom of the alkyl group and the oxygen atom of AGES. NEGS is depicted below as the ethoxylated sodium salt, EQU R(OCH.sub.2 CH.sub.2).sub.n OCH.sub.2 CHOH CH.sub.2 SO.sub.3.sup.- Na.sup.+(FIG. 2)
n is an average value of one or more. PA1 R is an alkyl or alkenyl group
The synthesis of AGES outlined above involves functional group transformation, the conversion of an epoxide to a hydroxy sulfonate. Since the same functional group transformation occurs in the preparation of NEGS, the advantages and disadvantages occurring in the AGES synthesis outlined above would also be expected in a NEGS synthesis using the same process.
Surprisingly this does not occur to the extent expected. Rather, several significant advantages occur when the ethoxylated alkyl terminal epoxy is reacted preferably with a mixture of sulfite-bisulfite salt.
Firstly, the reaction can be carried out at room temperature or elevated temperature below 100.degree. C., the boiling point of water, without the use of elevated pressure. This brings about lower processing costs and allows the surfactant to be made in the same type of "kettle" or "crutcher" like equipment in which a personal cleansing composition can be prepared. For the synthesis of AGES, a substantially elevated temperature, below about 300.degree. F., is used to initiate the sulfonation conversion of the glycidate to the hydroxy sulfonate structure via the sulfite-bisulfite reaction. However this present conversion of the NEGS glycidate is initiated and proceeds to completion at temperatures which are at or below the boiling point of water. In fact, even though the reaction is exothermic, the reaction temperature can be maintained at or below about 110.degree. C., preferably at or below 100.degree. C. Such lower temperatures eliminates the need for pressure reactors or the addition of water.
Secondly, when converting the glycidate of AGES with alkali metal sulfite-bisulfite, the viscosity increases as the percent solids of products increases according to the cautionary statements of the Whyte article. However, when preparing NEGS from a terminal glycidate (epoxy) starting material the viscosity of the reaction mass measured at completion of the reaction, greater than about 50 wt % to about 75 wt % solids content remains essentially unchanged or is reduced from the viscosity at or about 50 wt %. This is an important factor in allowing preparation of a higher percentage NEGS product in water. Such a high solids content provides major advantages in handling, cost savings in transport, and processing the NEGS through adequate mixing into a cleansing composition.
Thirdly, the sodium salt(s) of a sulfite-bisulfite mixture can be employed and still see the higher solids, processable composition. Such higher solids content was previously thought to be achievable or potentially achievable only through the use of the potassium salt according to the review article. However potassium salts of a surfactant brings about a much softer and difficult to process solid personal cleansing composition than a sodium salt composition.
Fourthly, a catalytic quantity of an emulsifying agent, in the NEGS reaction brings about a shorter induction time and shortened total reaction time than the similar or same agent employed in a comparable AGES reaction.